Gaseous effluent treatment apparatus

ABSTRACT

The invention relates to an apparatus for the treatment of gaseous effluents, such as those originating from the production of semi-conductors involving contact with a liquid. The inventive apparatus consists of: a gas/liquid contact chamber which can receive a liquid in the lower part thereof and which is topped with a gas cover, said chamber comprising means for introducing a gas to be treated and means for releasing residual gases following treatment involving contact with the liquid; turbine-type gas/liquid contacting means comprising one or more stages which ensure improved contact between the gas and the liquid, the upper part of said means being equipped with an opening for drawing the gas situated in the gas cover above the liquid; and, preferably, means for measuring the pH of the liquid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of pending application Ser.No. 10/592,336 filed Sep. 11, 2006, which is a national stage entryunder 21 USC §371 of PCT/FR200605019 filed Mar. 30, 2005, which claimspriority to French application 0450640 filed Mar. 31, 2004, the entirecontents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to an apparatus for treating gaseouseffluents by contact with a liquid.

In a semiconductor production line, vacuum pumps are often connected todeposition or etching reactors which, during phases in which themanufacturing process is implemented, release toxic and corrosive gasessuch as HF, F₂, HC, Cl₂, NH₃, etc. These gases are highly corrosive andtherefore raise problems in the design and construction of the effluenttreatment and destruction circuits, problems which are difficult tosolve, particularly concerning the choice of materials to be used.

In order to treat the gases or fluids thus issuing from these machinesat the source, that is, at the outlet of the vacuum pump, it isnecessary to have compact apparatus which can be installed directlyunder the deposition and/or etching reactors of the circuits, andparticularly under the drop ceilings of the white rooms according to thecurrent design of these white rooms.

In order to solve the problem thus posed, the apparatus for treatinggaseous effluents according to the invention is characterized in that itcomprises:

-   -   a gas/liquid contact chamber for receiving a liquid in its lower        part, surmounted by a gas overhead, said chamber comprising        means for introducing a gas to be treated and means for removing        the waste gases after treatment by contact with the liquid,    -   gas/liquid contacting means of the turbine type, for ensuring        improved contact of the gas with the liquid, said means        comprising an opening in their upper part, for drawing out the        gas from the gas overhead above the liquid, preferably, means        for measuring the pH of the liquid,    -   optionally, means for changing and/or controlling the pH of the        liquid.

Preferably, the apparatus of the invention further comprises means forremoving the liquid after a predefined period.

Also preferably, it comprises demisting means for trapping the liquiddroplets in the waste gases discharged, said means being connected tothe means for removing the gas to be treated.

The gas/liquid contact chamber preferably comprises antivortex walls andcan thereby, for example, be made in the form of a parallelepiped-shapedchamber.

Various exemplary embodiments are possible:

-   -   If no negative pressure is useful or necessary for the device        placed upstream of the apparatus of the invention, the means for        introducing the gas to be treated are placed in the lower part        of the gas/liquid contact chamber, in order to inject the gas        into the liquid when the apparatus is in operation. These means        for introducing the gas to be treated are preferably placed,        with respect to the gas/liquid contacting means, so that when        the gas to be treated is injected into the liquid, the gas        bubbles created pass into the field of action of said contacting        means,    -   If a slight negative pressure, for example, between −10 mbar and        −500 mbar gauge, is useful or necessary for the equipment placed        upstream, it is preferable to inject the gases to be treated        directly into the gas overhead of said apparatus, to take        advantage of the natural suction capacity, created by the        gas/liquid contacting means, particularly in the case, for        example, of a hollow-shaft turbine.    -   If a higher negative pressure is required by the upstream        equipment, for example, between −50 and −500 mbar, or a more        intensive trapping of the solids, for example, of the reaction        byproducts produced upstream of the apparatus, an injector can        be placed in a scrubber inlet line. This injector may be        supplied in two ways: by a submersible pump mounted on the same        shaft as the turbine, or by a second submersible pump unit        juxtaposed with the turbine device.

According to a preferential embodiment of the invention, the gas/liquidcontacting means comprise an upper part not immersed in the liquidduring the operation of the apparatus, said upper part comprising anopening connected to suction means for drawing off the gas overheadlocated above the liquid and for reinjecting it into the liquid. Forexample, the contacting means may consist of a rotary “turbine” typedevice which, by its rotation in the liquid (about the vertical shaft towhich it is connected, shaft driven by a motor actuated by any means)creates a negative pressure in the line to which the turbine isconnected. This “turbine” device is designed to draw out the gases fromthe gas overhead above the liquid via its hollow shaft, for exampleusing an opening in the upper part, and to inject the same gases intothe liquid via the hollow turbine at the hollow shaft end.

According to a variant of the invention, this device serves to partiallyrecycle the gases before discharge, in order to scrub these gasesseveral times in the liquid.

Preferably, the gas/liquid contacting means consist of a turbineimmersed, in operation, in the liquid and rotating about a verticalaxis. This vertical axis may, for example, be off-centered in thegas/liquid contact chamber.

The gas/liquid contacting means may consist, for example, of a surfaceturbine (which draws the liquid from the bottom of the chamber intocontact with the gases at the surface) or a turbine located deep in theliquid (which draws the gases at the surface to inject them into theliquid).

The invention will be better understood from the following nonlimitingexemplary embodiments in conjunction with the figures which show:

FIG. 1, a general view of the apparatus of the invention,

FIG. 2, a schematic cross-sectional view of the apparatus in FIG. 1 inits atmospheric version, that is, with injection of the gas to betreated into the liquid,

FIG. 3, a graphic representation of the turbine suction capacity as afunction of the motor rotation frequency,

FIG. 4, a graphic representation of the CO₂ gas destruction/conversionrates as a function of the flow rate of gas to be treated,

FIG. 5, an exemplary embodiment of the invention as shown in FIG. 2,comprising additional means for increasing the gas/liquid mixing,

FIGS. 6 a and b show another exemplary embodiment of FIG. 2 withsubatmospheric injection of the gas into the gas overhead located abovethe liquid,

FIG. 7 shows a variant of FIG. 2 comprising two stages for dispersion ofthe gas to be treated in the liquid,

FIG. 8 shows another variant of FIG. 2 comprising three stages fordispersing the gas to be treated in the liquid.

The apparatus shown in FIGS. 1 and 2 will now be described. Thisapparatus comprises:

-   -   a gas/liquid contact chamber 1 of preferably parallelepiped or        otherwise cylindrical shape, but equipped with antivortex walls,        made from a corrosion-resistant but preferably inexpensive        material like, for example, polyvinyl chloride or polypropylene,    -   a gas/liquid contactor consisting of a motor-driven bottom        turbine, a hollow shaft 6 and hollow blades 7. The gas to be        treated is injected either via the inlet orifice 15 directly        into the liquid, or into the gas overhead above the liquid. In        some cases, a vertical tube of the same diameter as the turbine        may be installed, drawing the liquid from the bottom of the        chamber, thereby improving the homogeneity of the treatment        liquid and hence the treatment efficiency. The blades 7 of the        turbine are connected to the vertical hollow shaft 6 which        extends to 8,    -   a pH meter (or more: 9 and 10 in FIG. 1) for controlling the pH        of the treatment solution, as required, either by the injection        of water (inlet 13), caustic soda or acid (inlet 14) preferably        by a servocontrolled proportioning pump,    -   a valve for draining the treatment effluent (not shown, FIG. 1),        to a storage unit or the settling and neutralization station,    -   a gas outlet in the gas overhead for removing the treated gas to        the conventional (adsorption) discharge and final treatment        circuits,    -   a demister to trap the water droplets in suspension in the gas        just before discharge into the conventional circuit for treating        the usual acidic gaseous effluents (CO₂, etc.).

FIG. 2 shows a cross-section of the device in FIG. 1.

The gas/liquid contact chamber 101 is filled with water 138 (or anyother appropriate liquid desired) to a level 139 without mixing, belowthe suction 140 of the turbine 106, 107 in the gas overhead 141 abovethe liquid level 139.

A bearing 133 traversed by the vertical shaft 106 of the turbine andconnected to the gear wheel 105, serves to transmit the rotary movementto the turbine 107 via a notched belt 104, and a gear wheel 103 directlymounted on the motor 102.

The gas to be treated is injected at 117 via the line 116 into the lowerpart 115 of the parallelepiped-shaped chamber 101 (for the atmosphericvariant of the scrubber), the gas entering at 115 into the chamber 101is injected into the field of action of the turbine 107, of which thestrong stirring generates an effective transfer area of the gas by finedispersion into the liquid 138.

The gas after treatment (that is after several circulations in the waterin the atmospheric variant of the scrubber, passage into the gasoverhead, suction from the gas overhead and reinjection into the bottomof the bath by the turbine 107), is removed via the opening 112, theline 118, the passage on a demister 119 to remove the excess moisture,followed by passage into the cavity 121 and escape via the orifice 120(to dry treatment or directly to the atmosphere, as required). Thecavity 121 comprises a discharge system 122 and the valve 125 of thetrapped liquid which flows to the gravity drain line 126. A line 123 isconnected to the same drain 126 via the valve 124. This circuit permitsthe removal from the branch 143 of the surplus liquid flowing from 121via 124 and 123 necessary for stabilization in the liquid compositionand the removal of excess suspended matter.

A pressure sensor 142 is placed in the gas overhead 141 to monitor thepressure above the liquid and to avoid overpressures.

Deionized water is injected at 130 via two branches: the valve 134 andthe line 135 (make-up of drained liquid by water or fresh product) andthe valve 132 and the line 131, followed by injection at 136 afterpassage through 133 (lubrication of the upper bearing of the turbineshaft).

The operation of the system described in FIGS. 1 and 2 is explainedbelow.

The chamber filled with water is equipped with a surface or bottomstirring turbine designed to increase the gas/liquid transfer area toaccelerate the absorption of the corrosive gases in the treatmentsolution. To improve these exchanges, the treated gas is directlyinjected under the stirring turbine (in the specific case of theatmospheric variant of the scrubber). In the case in which a surfaceturbine is used, according to a variant of the invention, betterstirring is obtained by drawing the water from the bottom using avertical tube (or by adopting a solution described in FIG. 5). Thetreated gas is removed to the central treatment circuit, in the case ofsemiconductor production, via a hydraulic valve and a demister.

Depending on the pollutants to be removed, the pH of the treatmentsolution can be adjusted by adding basic product or only water,servocontrolled by the pH control. It should be observed that for analkaline gas like NH₃, the injection of caustic soda is useless, and thepH control can be used to inject water. The drainage of the treatmentsolution is preferably controlled both by the pH control and the levelcontrol. The spent solution is removed either to a storage unit or to aneutralization station.

Among the advantages of the invention described above, mention can bemade in particular of: the versatility of such an apparatus because itserves to treat very different pollutant fluids or gases, while causinga very small pressure drop in the chamber, that is, causing nodisturbances in the operation of the vacuum pumps installed at theoutlet of the semiconductor deposition or etching chambers.

The power consumption for such a system has proved to be low (about 50to 500 watts) and a compact geometry can be devised to make thisapparatus installable under the drop ceiling of the white rooms.

FIG. 3 shows an example of the suction capacity of a turbine of theinvention as a function of the motor rotation frequency. The treatmentcapacity of the apparatus of the invention can thereby be easilyadjusted by increasing the rotation frequency of the motor, since thiscapacity is multiplied by a factor of about 6 for a frequency increaseof about 2.5.

FIG. 4 shows an example of a graphic representation of the CO₂ gastreatment rate with water as a function of the flow rate of gas to betreated for an inlet concentration of 2500 ppm of CO₂ in the gas to betreated and a suction flow rate of 300 liters per minute thanks to theturbine. Thus, for a flow rate of 50 liters per minute, the destructionrate of carbon dioxide obtained is 95%, dropping to 70% for a flow rateof 200 liters per minute of gas to be treated.

In applications requiring higher destruction rates (ORE), use can bemade selectively of the multistage options described below (the turbinesolution alone in FIG. 2 constituting the common single stage base) inFIGS. 6, 7 and 8.

FIG. 5 shows a modification of the system described in FIG. 2, making itpossible, if necessary, to increase the gas/liquid contact efficiencyand thereby increase the destruction/treatment rate of gas entering theapparatus of the invention, particularly in the case in which theturbine is close to the surface. For this purpose, a housing 140 may beprovided, covering the turbine 107 and which extends to a level belowthe gas outlet of the turbine 107, with the optional addition of fins141 integral with the turbine shaft 106. These fins improve the stirringin the liquid and thereby favor the material transfer, said fins alsoallowing the discharge of the mixture to the bottom of the receptacle(according to their orientation) thereby lengthening the residence timeand increasing the gas-liquid exchange in the ressel. Obviously, toallow gases to enter the mixing chamber, it may be possible (not shownin the figure) either to connect the end 115 of the line 116 directly tothe inlet of the housing 140, or, more simply, to provide one or moreopenings in the housing. This variant of the invention with a protectivehousing around the turbine and/or the system of fins 141 forming apropeller which discharges the mixture to the bottom of the receptacle,is obviously applicable to the variants in FIGS. 6, 7 and 8 below.

The apparatus described in FIG. 6 corresponds to the case in which aslight negative pressure is necessary or preferable to improve theoperation of the gaseous effluent plasma destruction apparatus placedupstream of the apparatus of the invention. Furthermore, the suctionserves to reduce the inline pressure drop of the gas-scrubbing apparatusaccording to the invention. In this figure, the same elements as thosein the preceding figures bear the same reference numerals.

The gas overhead above the liquid is under slight negative pressure whenthe motor rotates the turbine. The gases to be treated are injected intothe gas overhead, drawn via the opening in the turbine axis, dischargedinto the liquid via the ends of the turbine, and then recirculated inthe vessel and re-drawn via the opening in the turbine axis, etc.However, part of these gases escapes in the “water seal” 701 which isbetter shown in FIG. 6 b. This water seal has the shape of a pipe, forexample cylindrical 701, with diameter d, placed inside the receptacle702, for example cylindrical also, of diameter D. In practice, it isimportant to determine a good compromise of the d/D ratio to obtain goodmaterial transfer efficiency and to avoid drawing out all the gasespresent in the gas overhead (so that they can be recycled several timesthrough the treatment liquid). To find the best compromise, it sufficesto perform a few tests with pipes 701 of different diameters and torecord the destruction rates obtained. The bottom end 703 of the tube701 must be immersed in the liquid to permit this pressure differentialbetween the gas present in the upper part of the pipe 701 and which isdischarged toward the outlet, and the gas which constitutes the gasoverhead above the liquid in contact with the gas inlet in the treatmentreceptacle.

FIGS. 7 and 8 show variants of the embodiment in FIG. 2, correspondingto destruction rates (DRE) higher than the one supplied by the apparatusin FIG. 2.

The example described in this FIG. 6 corresponds to the case of a slightnegative pressure of about 10 to 50 mbar (1 to 5×10³ pascal).

FIG. 7 shows a subatmospheric variant of the apparatus of the invention,comprising two stages for dispersing gas to be treated in the treatmentliquid. The gas, injected into the gas overhead above the liquid, isdrawn out by the treatment liquid in a hydro-injector type of device.

In general, a person skilled in the art will find all the necessaryinformation concerning the equipment to be used in the book by P. Perryet al. entitled “Perry's Chemical Engineer's Handbook, 6^(th) Edition”,particularly page 20-97 (this was.

The liquid fed to this hydro-injector originates from a submersible pumpplaced under the turbine and connected to the drive shaft of theturbine. The rotation of the drive shaft of the turbine causes therotation of the vanes 715 of the submersible pump 714. The liquid issucked out via an opening 716 under the pump 714.

According to a variant of the invention, the pump can be placed outsidethe treatment vessel, that is, not immersed.

A line, for example, cylindrical 717 surrounds the hydro-injector 710 atthe outlet of the gas/liquid mixture in order to limit the lateralexpansion of the outgoing jet of gas/liquid mixture. The liquid returnsby gravity to the liquid bath, the part of gas unreacted with the liquidin the hydro-injector returning to the gas overhead to be drawn outagain at the suction inlet 140 at the shaft of the turbine. Thedimensions of the line 717 must be limited in order to control thepressure drop and to obtain a higher negative pressure, of about 50 to500 mbar (or 5×10³ pascal to 5×10⁴ pascal).

As in FIG. 6, a discharge line 701 is provided for the treated gasesissuing from the liquid.

As previously, the liquid used has a pH adapted to the gas to be treated(hence generally a pH>7 for generally acid gases) to obtain the desiredchemical reaction, or simply water (from the mains at pH 7) in which thegases are absorbed in the liquid. As previously, means are provided formeasuring the pH and, optionally, means for controlling it, bymaintaining it in a range of predefined values, either by addingadditives of opposite pH, or by replacing the solution when it becomesoff-specification (outside range).

To improve the gas/liquid exchange, it may be preferable to blendsurfactants with the liquid, particularly water, in small quantities toavoid foaming, so as to decrease the size of the gas bubbles andincrease the gas/liquid exchange area.

The variant of the embodiment in FIG. 8 corresponds in particular to athree-stage gas/liquid exchange system, comprising, in addition to thetwo stages shown in FIG. 7, a third stage comprising an exit line 700 ofthe submersible pump 716, which sends part of the liquid drawn by thepump 716 to the exit line 701, projects it on a deflector 720, forexample, whose function is to lower this liquid in a countercurrentspray to the gas issuing from the liquid (from the gas overhead)preferably in the form of a flat circular jet. According to anothervariant of the embodiment, a static mixer can also be connected,connected at its other end to the external discharge of the gases aftertreatment. An example of appropriate static mixers is described, forexample, in the work by W. L. McCabe entitled “Unit Operations ofChemical Engineering” 5^(th) Edition.

FIG. 8 also shows a level detector 800 for detecting the level of fluid801 recovered in the demister, this detector controlling the drainage atthe gravity drain 128 via the controlled valve 125 and the line 122.Similarly, the drainage of the vessel is controlled by the pH detector740 which opens the drain valve via 123 and 126.

According to the invention, the gas/liquid contacting means provideenergy (motor driven means) in order both to produce a compact systemgenerating very little pressure drop or no or negative pressure drop,such a system, by a pumping effect, improving the circulation of thegaseous effluents in the gaseous effluent discharge lines.

According to another variant of the invention, a system known per se andcalled a hydro-cyclone can be provided, for separating the solid phasefrom the liquid phase of the liquid after use in the vessel. Such asystem serves to recycle the water thus cleansed of its solids, to theapparatus of the invention.

It will be understood that many additional changes in the details,materials, steps and arrangement of parts, which have been hereindescribed in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims. Thus, the presentinvention is not intended to be limited to the specific embodiments inthe examples given above.

1. An apparatus for treating gaseous effluents by contact with a liquid,wherein it comprises: a) a gas/liquid contact chamber for receiving aliquid in its lower part, surmounted by a gas overhead, said chambercomprising means for introducing a gas originating from the productionof semiconductors and means for removing the waste gases after treatmentby contact with the liquid; b) gas/liquid contacting means for ensuringimproved contact of the gas with the liquid, said means comprising anopening in their upper part, for drawing out the gas from the gasoverhead above the liquid, wherein the gas/liquid contacting meansconsist of a surface turbine; and c) means for measuring the pH of theliquid.
 2. The apparatus of claim 1, further comprising means forchanging and/or controlling the pH of the liquid.
 3. The apparatus ofclaim 1, further comprising demisting means for trapping the liquiddroplets and connected to the means for removing the waste gases aftertreatment.
 4. The apparatus of claim 1, wherein the gas/liquid contactchamber has a parallelepiped or cylindrical shape.
 5. The apparatus ofclaim 1, wherein the means for introducing the gas to be treated areplaced in the lower part of the gas/liquid contact chamber, in order toinject the gas into the liquid when the apparatus is in operation. 6.The apparatus of claim 1, wherein the means for introducing the gas tobe treated are placed in the upper part of the gas/liquid contactchamber, in order to inject the gas into the gas overhead when theapparatus is in operation.
 7. The apparatus of claim 1, wherein thegas/liquid contacting means comprise an upper part not immersed in theliquid, during the operation of the apparatus, said upper partcomprising an opening connected to suction means for drawing off the gasoverhead located above the liquid and for reinjecting it into the liquidin order to circulate the gas constituting the gas overhead severaltimes in the liquid.
 8. The apparatus of claim 7, wherein a lineconveying the gas drawn out of the gas overhead and injected into theliquid via the turbine has an axis parallel to or merged with the axisof rotation of the turbine.
 9. The apparatus of claim 1, wherein the gasto be treated is injected into the liquid via a hydro-injector.
 10. Theapparatus of claim 9, wherein a line surrounds the hydro-injector tolimit the lateral expansion of the jet.
 11. The apparatus of claim 9,wherein the hydro-injector comprises a submersible pump whichrecirculates the liquid via a line connected to the hydro-injector. 12.The apparatus of claim 1, further comprising a submersible pump whichsends the liquid to an exit line connected to the gas overhead above theliquid bath, in which is placed a deflector which sprays the liquid jetissuing from the pump in countercurrent to the gases removed via theexit line.
 13. The apparatus of claim 1, wherein the means for measuringthe pH of the liquid controls a valve for removing the liquid solutionto a drain.